The present invention relates to a surface treating method of an aluminum alloy casting, for example, and to a treating member therefor.
Recent years, the highest compression pressure within a combustion chamber has increased from about 120 kgf/cm2 to about 150 kgf/cm2 with an increase in power of diesel engines used for automobiles, so that the heat load applied to an aluminum alloy casting such as a cylinder head constituting the chamber has also increased. Therefore, a remelt treatment has locally been performed (for example, between adjacent ports (a space between valves)) in order to improve heat resistance to thermal fatigue or thermal stresses (see FIG. 30). Further, the depth of the remelt portion being required has also become greater than before.
FIG. 34 is a flowchart illustrating a manufacturing process of a cylinder head used for a conventional diesel engine. FIG. 35 is a schematic diagram illustrating the remelt treatment in the manufacturing process of FIG. 34.
At step T1, the cylinder head, as an intermediate, is cast as illustrated in FIG. 34. At step T2, the casting is removed from a mold, then a sprue gate is cut. At step T3, the casting is subjected to a T6 heat treatment mainly for the purpose of sand stripping. At step T4, pre-processing for the remelt treatment is conducted. At step T5, the cast is pre-heated. At step T6, the space between valves of the cast is subjected to the remelt treatment. At step T7, the cast is subjected to the T6 heat treatment again. At step T8, a finish processing is conducted.
In the remelt treatment, as shown in FIG. 35, the cast which was subjected to the sand stripping is pre-heated, then an electrode is brought close to the region to be surface-treated and is moved while producing a TIG or plasma arc between the electrode and a member to be surface-treated, in order to melt a texture to be treated to a predetermined depth and to solidify the texture again. Therefore, this treatment has effects of making the metal texture finer and of increasing its elongation by achieving a reduction of casting defects. Further, the residual stress which is caused by the remelt treatment is released by performing the T6 heat treatment again after the remelt treatment. In the remelt treatment, the metal texture is made finer by increasing a cooling rate during the re-solidification.
As another surface treating method, Japanese Patent Application Laid-Open No. 7-88645 discloses a structure which enhances its adhesion with a base material and intends to improve resistance to thermal fatigue, by means of padding an Alxe2x80x94Cu based alloy having a higher solidus than the base material to the space between valves in order to form a high strength layer.
Further, though in a different technical field than the surface treating technology, Japanese Patent No. 2712838 discloses a welding technology wherein probes are inserted while being rotated into joint surfaces of the two members and translated, then the metal textures which are close to the joint surfaces are plasticized by the frictional heat and bonded to each other.
Still further, Japanese Patent Application Laid-Open No. 10-183316 and Japanese Patent Application Laid-Open No. 2000-15426 disclose a method for treating the surface of a cast, such as an abutting surface for a cylinder block of a cylinder head, wherein a rotating tool whose end portion has a shoulder portion provided with a protrusion is squeezed while being rotated into the surface, then the surface is stirred with the heat in a non-melting state.
However, the above described remelt treatment imposes a restriction on the depth which is capable of being treated, because the shoulder die wear is caused by over-melting due to the small heat capacity of the space between valves, even when an amount of heat input is increased for the purpose of increasing the treating depth such that the depth is adapted to an increase of the heat load which is applied to the cylinder head. In addition, increasing the amount of heat input results in a long solidification time, so that the effect of making the texture finer becomes less and pinhole defects also increase. Therefore, an effect which is obtained by increasing the treating depth is cancelled out, so that it becomes difficult to obtain the intended effect of improving heat resistance.
Further, increasing the amount of heat input also results in the easy occurrence of cracks in the member due to the thermal stresses during the remelt treatment, so that the member is required to be pre-heated. In addition, a base material containing magnesium has a possibility of not providing the required mechanical characteristic because magnesium is vaporized and decreased at the time of melting and the reinforcement width strength improvement of the member becomes small due to the T6 heat treatment which is performed after the remelt treatment.
In terms of quality, ensuring a qualitative stability becomes a problem because the treating depth largely varies due to variations in the amount of heat input and displacements caused by the magnetic arc blow and because the pinhole defects in the treating portion is affected by the gas content of the base material and the blow hole coverage ratio.
In terms of productivity, a shielding gas is required for preventing the melting portion from being oxidized because the treating portion is melted, and further, a process of eliminating a cast surface before the treatment is added in order to prevent the defects caused by gases which are produced from surface oxides or impurities. In addition, a cost reduction has also become a problem because a post heat treatment is required for releasing the high tensile residual stress which is applied to the treating portion.
In addition, the padding which is described in the above publication has a productive problem of how to supply the materials used for this padding and a qualitative problem of suppressing the pinhole defects and ensuring the stability of the base material dilution rate. In addition, a problem caused by melting the base materials also exists as in the case of the remelt treatment.
On the other hand, in the above described Japanese Patent Application Laid-Open No. 10-183316 and Japanese Patent Application Laid-Open No. 2000-15426, treating paths are required to be appropriately set in order to process a large region with the use of a small protrusion while preventing deformation of the material.
The present invention has been made in view of the above described problems, and its object is to provide a surface treating method which can realize a deep treating region while preventing unfilled defects caused by the deformation of the material, and a treating member therefor.
In order to solve the above described problems and to achieve the object, a surface treating method according to the present invention is a surface treating method in which the surface of a cast having concave portions is stirred for refining without melting it by the heat from a rotating tool, wherein the surface treatment is performed such that, in a surface treating path of the above described rotating tool in a region which is in the closest vicinity of the above described concave portion, a material between the above described concave portion and the rotating tool flows in a direction opposite to the travel of the above described rotating tool.
In addition, the surface treating method according to the present invention is a surface treating method in which the surface of a cast having concave portions is stirred for refining without melting it by the heat from a rotating tool, wherein the surface treatment is performed such that, in a surface treating path of the above described rotating tool in a region which is in the closest vicinity of the above described concave portion, a material between the above described concave portion and the rotating tool flows in the same direction as the travel of the above described rotating tool.
In addition, the surface treating method according to the present invention is a surface treating method in which the surface of a cast subjected to the perforating is stirred for refining without melting it by the heat from a rotating tool, wherein the surface treatment is performed such that, by the use of the rotating tool whose diameter is smaller than that of a hole created by the above described perforating, a terminal point of a surface treating path created by the above described rotating tool becomes a position which is subjected to the above described perforating.
And preferably, a plurality of the above described concave portions exist, regions between the above described concave portions are refined by the above described rotating tool, and the above described surface treating paths are set such that the above described refined regions are overlapped.
And preferably, the terminal point of the above described surface treating path is set such that the path passes through the start point of the above described surface treating path.
And preferably, the above described cast is a cylinder head having a pair of intake ports and a pair of exhaust ports corresponding to a plurality of cylinders, a continuous treatment is carried out along a longitudinal direction of the above described cylinder head and between the above described pair of exhaust ports and the above described intake ports, and subsequently the surface treatment is carried out from a cylinder adjacent to the position and between the above described exhaust ports and intake ports.
Further, a surface treating member according to the present invention is a treating member which has concave portions and the surface of which is stirred for refining without melting it by the heat from a rotating tool, wherein the surface treatment is performed such that, in a surface treating path of the above described rotating tool in a region which is in the closest vicinity of the above described concave portion, a material between the above described concave portion and the rotating tool flows in a direction opposite to the travel of the above described rotating tool.
Further, the surface treating member according to the present invention is a treating member which has concave portions and the surface of which is stirred for refining without melting it by the heat from a rotating tool, wherein the surface treatment is performed such that, in the surface treating path of the above described rotating tool in a region which is in the closest vicinity of the above described concave portion, a material between the above described concave portion and the rotating tool flows in the same direction as the travel of the above described rotating tool.
Further, the surface treating member according to the present invention is a treating member which is subjected to the perforating and the surface of which is stirred for refining without melting it by the heat from a rotating tool, wherein the surface treatment is performed such that, by the use of the rotating tool whose diameter is smaller than that of a hole created by the perforating, a terminal point of a surface treating path created by the rotating tool becomes a position which is subjected to the perforating.